The dendrites of many neurons contain voltage-gated channels that turn otherwise passive structures into electrically excitable dendrites. Dendritic excitability enables backpropagation of action potentials from the soma into the dendritic tree and the initiation of spikes in the dendrite and these phenomena play important roles in synaptic integration and in synaptic plasticity. Dendritic excitability has been studied extensively in brain slice preparations and to a lesser extent in anesthetized animals, but little is known about dendritic excitability in awake animals. To understand how ongoing synaptic activity affects synaptic integration and plasticity in vivo, in this project we will directly measure dendritic excitability in awake animals using whole-cell recording and two-photon imaging techniques, using the extent of propagation of action potentials into the dendritic tree as a measure of dendritic excitability. Since these are the first studies to use these high-resolution techniques in awake animals, our studies will provide unprecedented information on dendritic function in awake animals.